Register indicating system

ABSTRACT

Multi-unit machine for operating on sheet material in web form or in the form of individual sheets with the operations performed by each unit to be in precise registry with the operations performed by the other units. Each unit applies a register mark to the sheet material which has a fixed position relative to the operation of the unit on the sheet material. The register marks are scanned as a group to provide output signals for checking the timing of the units. The output signals are pulses which are combined to provide a predetermined pulse pattern when the units are in registry and different pulse patterns when one or more of the units is out of registry. A cathode ray tube is utilized to display the pulse patterns.

United States Patent Richardson Apr. 4, 1972 [54] REGISTER INDICATING SYSTEM [72] Inventor: James Ivor Richardson, Montville, NJ.

[73] Assignee: Harris-Intertype Corporation, Cleveland,

Ohio

[22] Filed: Aug. 5, 1969 21 Appl. NOL; 847,611

' 52 us. c1 ..101/24's, 101/181 [51] Int. Cl. [58] Field ofSearc ..101/18l,248;250/219 DR; 9 226/100; 340/1463 l 56] References Cited UNITED STATES PATENTS 2,289,737 7/1942 ,Sorkin.... -.....l01/181X 2,356,567 8/1944 Cockrell 50/219DR X 2,361,549 10/1944 Kott 250/219 DR X 2,583,580 l/1952 Ludwig.. ..101/181X 2,616,961 11/1952 Groak.... .....10l/181 X 2,768,827 10/1956 Noble ..10l/181 3,084,621 4/1963 Gustavino ..101/248 X VERT/CAL EC T/O/V 3,213,422 10/1965 Fritze ..340/146.3 3,264,983 8/1966 Lewis 101/ l 81 3,339,817 9/1967 French. ....226/100 3,452,872 7/1969 Canning ..73/147 X Primary ExaminerRobert E. Pulfrey Assistant Examiner-R. E. Suter Attorney-Yount and Tarolli [57] ABSTRACT Multi-unit machine for operating on sheet material in web form or in the form of individual sheets with the operations performed by each unit to be in precise registry with the operations performed by the other units. Each unit applies a register mark to the sheet material which has a fixed position relative to the operation of the unit on the sheet material. The register marks are scanned as a group to provide output signals for checking the timing of the units. The output signals are pulses which are combined to provide a predetermined pulse pattern when the units are in registry and different pulse patterns when one or more of the units is out of registry. A cathode ray tube is utilized to display the pulse patterns.

15 Claims, 5 Drawing Figures PATENTEB APR 4 I972 SHEET 2 BF 2 Mk? NW? Wk? NW? 5 ZCQQGQE Q EEEW (Kit REGISTER INDICATING SYSTEM The present invention relates to an apparatus and method for ascertaining the registrations of operations being performed on sheet material in the form of a web or individual sheets by a plurality of machine units through which the sheet material moves in sequence. The invention is particularly useful in a printing press in which each of the units applies an image to the sheet material moving through the unit with the image being repeated on succeeding material to form successive images as the material passes continuously through the machine. Each of the images printed by a unit is to bear a predetermined relationship with respect to the images printed by the other units. For example, the printing apparatus may be a multi-color lithographic printing press in which each printing unit prints a respective component color image of a desired print onto the web or sheet. The component color images printed by the units are superimposed on each other to produce the desired print and must be in precise registry to produce a high-quality print.

In the practice of the present invention, each printing unit applies a register mark to the sheet material with the register mark having a predetermined fixed position with respect to the image printed by the unit. In a case of a printing press, the register mark maybe a part of a printing plate so that it is always in a predetermined position with respect to the image carried by the plate regardless of the position of the plate on the plate cylinder and regardless of the angular position of the printing unit relative to the other units.

The marks printed by the different units of the press corresponding to one image provide a group of register marks which are, when the images are properly registered, spaced from each other along a line extending in the direction of movement of the web or sheets through the printing press. The register marks of a group preferably all have the same spacing from their adjacent marks, with the spacing of each mark from the first mark being a multiple of the basic spacing between marks. The marks are preferably in the order of the printing units with the first register mark of a group corresponding to the first printing unit. If an image being printed by one of the units is not in registry, the spacing of its register mark from the other register marks will be different from the predetermined spacing which indicates register.

In accordance with a specific form of the invention, the register marks are sensed by a plurality of sensing devices which correspond in number to the number of units to be checked for register. The sensing devices are spaced from each other along the web or sheet path in accordance with the predetermined spacing between register marks of a group when the images being printed are in register. The outputs of the sensing devices are pulse signals generated by the movement of the marks past the sensing device. These pulse signals are combined so that when the units are in register, the pulse signals will increase and then decrease in magnitude as a group of register marks passes the sensing devices. In a lithographic press, a group of register marks comprises a mark printed by each unit as it prints an image. As a group of such marks corresponding to one final image passes the sensing devices, the first sensing device will have output signals in sequence in response to the arrival of the successive register marks and the other sensing device will have corresponding pulse output signals, but the output signals will be phase displaced by the time required for the register marks to move between the sensing devices. Consequently, as a group of register marks moves by the sensing devices, the first sensing device will have an output and this will be the sole output from the sensing devices. As the first register mark moves opposite to the second sensing device, the second register mark will be opposite the first sensing device and the combined output will have a magnitude which is the sum of the output signals from both the first and second sensing devices. When the first register mark moves opposite the third sensing device, the

' second register mark will be opposite the second sensing device and the third register mark will be opposite the first sensing device and the combined output will be a signal which is three times the magnitude of the initial signal. Similarly, as the number of register marks opposite the sensing devices increases, the magnitude of the combined pulse signals will increase, while after the first register mark passes the last sensing device, the combined pulse signal will start to decrease in magnitude. The magnitudes and the timing of the combined pulse signals from the sensing devices are utilized to indicate the registry of the images printed by the units.

An object of the present invention is to provide a new and improved system for checking the registry of machine units which operate in sequence on sheet material in which each unit applies a register mark which has a fixed relationship with respect to the operation performed by the unit on the material and the register marks are read by register mark sensing devices whose outputs are analyzed as a group to obtain an indication of the registry of the units.

A further object of the present invention is to provide a new and improved system for checking the registry of printing units, or other units for performing an operation on sheet material, with respect to each other in which an operator may view pulse signals whose patterns and form indicate when the units are in register and if the units are out of register the nature of the misregister.

Further objects and advantages of the present invention will be apparent from the following description of the specific form of the preferred embodiment thereof made in reference to the accompanying drawings and forming a part of this specification for all subject matter disclosed therein and in which FIG. 1 is a diagrammatic view of a printing press embodying the present invention;

FIG. 2 is a fragmentary showing of a printing plate used on one of the printing units of FIG. 1;

FIG. 3 is a sectional view taken approximately along line 3-3 of FIG. 1;

FIG. 4 is a view looking from approximately along line 44 of FIG. 3; and

FIG. 5 is a series of graphic displays illustrating output signals from the system.

The present invention can be used in and with various types of machines which have a plurality of units which are to operate on sheet material with the operation performed by the units to have a precise relationship on the material with respect to each other, e.g. printing presses and cutter and creasers operating with a plurality of units.

Referring to the drawings, the invention is illustrated as embodies in a four-color lithographic printing press 10 which is shown schematically in FIG. 1. The printing press includes four lithographic printing units 12, 13, 14 and 15 with each of the printing units having an impression cylinder 16, a blanket cylinder 17 and a plate cylinder 18. Printing presses of the type illustrated schematically in FIG. 1 are well known to those skilled in the art. It will be understood that each of the printing units includes the conventional dampening and inking mechanism and that the units print onto sheet material, such as a web 20 which is supplied from a web supply roll and which is delivered by conventional delivery means associated with the printing press.

In a multi-color lithographic printing press of the type shown, each printing unit prints a single-color image which is a color component of the final image to be printed onto the web. The color image printed by each of the printing units 12-15 must register precisely with the color images printed by the other printing units if the complete printed image is to be a high-quality print. It is understood that as the press operates, the images from the four printing units are superimposed on each other to make the final image and the final image is repeated along the length of the web once for each revolution of the printing units.

In a lithographic printing press, a plate carrying the image to be printed is mounted on the plate cylinder by plate attaching means located in the gap of the plate cylinder. In accordance with a specific form of the preferred embodiment of the present invention, the plates of each of the printing units have a register mark 22 thereon which is outside of the component image and along one side of the plate as illustrated in FIG. 2. The mark is in a fixed predetermined position with respect to the leading edge of the printing plate so that when the image is printed, a register mark 22a will also be printed onto the web, but outside of the picture or print area, at a fixed distance from the leading edge of the plate along one side of the web. The register marks for the printing units l3, l4 and are locatedfrom the leading edge of the plate at an increasingly greater distance. That is, the register mark on the plate on the unit 13 is at a greater distance from the leading edge of the plate than the register mark on the plate for the printing unit 12 and the register mark on the printing unit 14 is at a greater distance from the leading edge than the register mark on the printing plate for unit 13, etc. The spacings of the register marks from the leading edges of the plate are such that when the marks are printed onto the web, they are spaced equally along the length of the web when the images printed by the printing units are in precise registry along the length of the web. The register marks are short lines extending in a transverse direction across the web.

the units arein register. As shown in (a) of FIG. 5, the pulse minimum pulse signal designated by the reference character 45 which occurs when the first registration mark is opposite the sensing device 32a to a maximum pulse signal 47 which occurs when all four register marks are opposite to the sensing devices 32a 32d to a minimum pulse signal 49 when the last register mark is opposite the sensing device 32d.

Illustrative pulse patterns are shown in FIG. 5. Patterns (12) and (c) of FIG. 5 represent-typical pulse patterns when unit No. 1 is respectively advanced or retarded, (d) and (e) represent typical pulse patterns when unit No. 2 is advanced or retarded, (f) and (g) represent typical pulse patterns when unit No. 3 is advanced or retarded while (h) and (1') represent patterns for unit No. 4. From the examination of the patterns it will be seen that it can be readily determined when one unit is advanced or retarded. If only one unit is advanced or retarded, the pulse initiated by the mark printed by the unit when it reaches the first slit will cause the trailing or leading edge of thecombined pulses to be respectively advanced or retarded depending upon whether the unit is early or late in printing. If the. distortion first occurs in the third or fourth As the web leaves the last printing unit 15, the register marks are sensed by a sensing means comprising sensing devices corresponding in number to the number of printing units in the press, four in the illustrated embodiment. The sensing devices are shown in FIG. 3 and are designated by the reference characters 32a, 32b, 32c and 32d. The sensing devices 320 32d may be conventional photo detector devices for reading register marks on a web and, in the illustrated embodiment, have been shown as being responsive to light from a lamp 34 which extends along the web adjacent the sensing devices 32a 32d. The sensing means includes a reflector 35 for directing the light onto the web, so that the light is reflected from the web to the sensing devices 32a 32d. The sensing devices 32a 32d each view the web through a respective slit 38 in a masking member 39. When a register mark passes the respective slit, the light received by the sensing device is diminished substantially to provide an output signal. The signals from conventional photo detectors are normally negative going signals. These signals may be shaped in conventional pulse shaping circuits (not shown) and then summed in a summing amplifier 40 whose output has a magnitude which is dependent upon the sum of the magnitude of the inputs thereto. The signals from the sensing devices may be inverted by the pulse shapers or by the summing amplifier 40 to provide a positive going signal from the summing amplifier 40. When all four register marks ofa group, assuming the marks are in their proper relationship, are opposite the reading slits for the sensing devices 32a 32d, the output of the amplifier 40 is at a maximum and-is proportionately less when three marks, two marks, or one mark is opposite to the reading slits. Consequently, as the first register mark arrives at the sensing device 320, a minimum pulse signal will appear at the output of amplifier 40. If the first two units have proper registry, a pulse signal of approximately twice that magnitude will occur when the first register mark arrives at the photocell sensing device 32b and the second register mark at the photocell sensing device 32a. Similarly, the amplifier output will be at a third level and at a maximum level as 3 and 4 register marks respectively are opposite to the sensing devices 32a 32d. Since it takes a period of time for the register marks to travel between the reading slits for the sensing devices 32a 32d, the outputs from the amplifier 40 will be spaced in time, assuming the units are in registry with each other, and the output from the amplifier 40 will be a series of pulse signals.

In accordance with the invention, the output of the amplifier 40 is applied to a vertical deflection control circuit 42 (FIG. 1) for a cathode ray tube 43. Also, the signal from the sensing device 32a is applied to a horizontal sweep circuit 44 to initiate a horizontal sweep of the beam. The cathode ray tube 43 will display the pulse signals as shown in (a) of FIG. 5 when pulse, the pulse where the first distortion occurs indicates the unit which is out of register and the shifting of the leading edge of the pulse forwardly in time or the trailing edge later in time will indicate whether the unit is advanced or retarded. When the distortion appears in the second pulse for the first time, it is not always clear from the second pulse whether the No. 1 unit is retarded or advanced or the No. 2 unit is retarded or advanced since the first unit pulse always appears in the same position on the CRT if it is used to initiate the sweep of the cathode ray tube. However, if the large peak in the third pulse coincides in time with the larger peak of the third pulse in the display (a) for registered units, it indicates that the first and third units are in time but the No. 2 unit is out while if the large peak appears in time ahead or after the peak for the third pulse in the display for registered units, it indicates that the No. 1 unit is advanced or retarded. The face of the cathode ray tube may be marked to indicate the center lines for the pulses of a display showing registered units to facilitate analysis of the pulses. It should be further noted that the distortion of the pulses after the fourth pulse clearly gives an indication as to whether the No. 1 unit or the No. 2 unit is out of time. If the No. 1 unit is out of time, the distortion is lost for the last three pulses while if the No. 2 unit is out of time, the distortion is lost for only the last two pulses. Similarly for other patterns, the pulses after the middle pulse for the pattern will indicate the nature of the out of time relationship.

From the foregoing, it will be clear to those skilled in the art that the magnitude of the pulses and their distortion as well as the time shift of the leading and trailing edges of the pulses from the in-register display indicates the timing of the units with respect to each other and the units which are not on time. It will also be clear that there will be typical display patterns for a combination of units out of time and one such display pattern is shown in the (j) display in FIG. 5. In this display, it is assumed that the third unit is early and the fourth unit is late. Accordingly, by analyzing the characteristics of the pulses particularly the manner of distortion, including the pulse at which distortion is lost and the time that a pulse begins or ends relative to its maximum, the registry of the units can be determined. During operation, when an operator determines that a unit is out of registry, he operates conventional means to advance or retard the unit or units to bring the images in registry to each other.

While preferably the pulse output signals from the sensing devices are of approximately equal magnitude, it will be understood that the distortion and change of time of the leading and trailing edges of the pulses may be utilized to analyze registry even though the pulse magnitudes are not equal.

Preferably the printing press drives a DC. tachometer 50 which has an output applied to the horizontal sweep circuit 44 to vary the sweep rate with press speed to maintain a constant separation between pulses on the cathode ray tube for units in registry. If desired, the sweep circuit could be adjusted manually in accordance with press speed.

It will be appreciated that electronic circuits for measuring the pulse height and time are well known and that the pulse height and time can be analyzed automatically with conventional circuitry to automatically effect control of the registration ofthe units.

In the described embodiment, the first register mark initiated the sweep of the cathode ray tube. It will be understood that the sweep of the cathode ray tube could be initiated by a fiducial mark on the press and that all the units, including the first unit, could be registered with respect to that fiducial mark and the cathode ray tube could be graduated so that the pulses occur at a predetermined point on the face of the tube if the units are in registry. This, however, requires the registering of the first unit to the fiducial mark.

What is claimed is:

1. A method of checking the register of images applied to sheet material passing through a plurality ofN units of a multiunit printing apparatus with the images printed by each unit to be in precise registry with the images printed by the other units, applying a register marking to the material at each of said units with the register marking having a predetermined fixed position relative to the image applied by the unit to the material with the markings-applied by the units when the units are in precise registry with each other constituting a group of markings having a predetermined spacing relative to each other,- subsequently sensing different numbers of register markings of a said group at each of a plurality of sensing locations along the path of movement of the material as each of the markings move in sequence past each of the sensing locations with the sensing locations being spaced from each other in such a manner that different numbers of said markings ofa group arrive at said sensing locations in sequence and each marking of a group is sensed a plurality of different times with successive markings being sensed simultaneously at said plurality of sensing locations when the units are in registry to provide an output signal each time one or more register markings is sensed, using the signals derived from a sequential sensing of different numbers of markings of a group passing said sensing locations to signal the registry of the images and thereby the timing of the printing units relative to each other.

2. A method as defined in claim 1 wherein said signals are pulse signals, and wherein signals derived from a simultaneous sensing of said markings are combined to provide a combined pulse output for indicating registry.

3. A method as defined in claim 2 wherein the sensing of the first one of a group of register markings arriving at said sensing locations is used to initiate a display apparatus for displaying the combined pulses and their timed relationship with respect to each other with the number of pulses which are displayed each time a group passes said sensing locations being one less than twice the number of markings in a group.

4. A method as defined in claim 3 wherein there are N units and the marking of each unit is sensed N times.

5. A method as defined in claim 1 wherein the images of each printing unit are printed from printing plates and the register markings are on the printing plates of each unit.

6. A method as defined in claim 1 wherein the register markings are printed with equal spacing between the adjacent markings of a group when the units are in registry.

7. in a printing apparatus having a plurality of printing units through which sheet material to be printed passes, each of said units having an image carrying member which carries the image to be printed by the unit and each of said image carryingmembers having as part of the image carried thereby a register mark which is located in a predetermined position with respect to the image, the images printed by the individual units being superimposed on each other and the register marks on the image carrying members of the units being located on the image carrying member so that the register marks are printed adjacent the superimposed image along an imaginary line which extends lengthwise of the sheet material with the register marks having a predetermined spacing relative to each other when the units are printing in precise registry with each other, the register marks consisting of one mark for each unit as sheet material passes therethrough constituting a group of marks, sensing means comprising a plurality of sensing devices, one for each unit, located at respective locations along the path of travel of the sheet material with the sensing devices being spaced from each other by said predetermined spacing whereby each of said marks pass each of said devices in sequence and are sensed by each said device to provide an output signal in response to each mark with successive marks being sensed simultaneously by successive sensing devices when said units are printing in precise registry with each other, and electrical means responsive to said output signals generated by one group of marks passing all'of said devices for signaling the register condition and thereby the timing of said units.

8. A printing apparatus as defined in claim 7 wherein said signals are pulses and said electrical means comprises circuit means for summing the pulse outputs from said devices. I

9. An apparatus as defined in claim 8 wherein said electrical circuit means comprises a cathode ray tube for displaying said summed output and a sweep circuit activated in response to a pulse output signal from the sensing device first responsive to a register mark of a group of register marks.

10. An apparatus as defined in claim 8 wherein said electrical means comprises a cathode ray tube for displaying said summed pulses.

11. An apparatus as defined in claim 10 wherein said electrical means includes means responsive to the speed of the apparatus for maintaining the summed pulses in positions on the tube which are independent of the speed of the material moving through the apparatus.

12. A method of checking the registry of a plurality of N units operating for performing operations in sequence on material passing through the units, applying a respective register marking to the material with each of said units to thereby provide a group of markings for indicating the registry of the units, sensing the time of arrival of the markings as the markings arrive at a plurality of sensing locations corresponding in a number to the number of units with the marking applied by each unit being sensed a plurality of times in combination with different numbers of markings of said group of markings to provide a group of electrical signals which are analyzable to determine registry.

13. A method of checking the register of operations performed in sequence on material passing through a plurality of units of a multi-unit apparatus with the operations performed by each unit to be in precise registry with the operations performed by the other units, said method including the steps of applying a plurality of spaced apart register marks to the material as the material passes through the plurality of units of the multi-unit apparatus with the spacing between the marks varying as a function of variations in the registry operations performed by the units, generating a plurality of pulses having a time relationship which is a function of the spatial relationship between the register marks and the registry of the operations performed by the units, combining at least some of said pulses to form a combined pulse having a characteristic which varies as a function of variations in the time relationship between the combined pulses and which is indicative of the registry between the units, said step of combining at least some of said pulses includes the steps of combining a plurality of pulses to form a plurality of combined pulses each of which has a characteristic which varies as a function of the time relationship between the pulses which were combined to form it, forming a series of pulses which includes a plurality of said combined pulses and which has predetermined characteristics which vary with variations in registry between the units in a manner which is indicative of which unit of the plurality of units is out of registry upon a variation in registry, and sensing the predetermined characteristics of the series of pulses to units'when the units are in precise registry with each other constituting a group of marks having a predetermined spacing relative to each other, sensing each of the register marks of a group at each of a plurality of sensing locations along the path of movement of the material after said operations have been performed and as the marks move in sequence past each of the sensing locations with the sensinglocations being spaced by said predetermined spacing with successive marks being sensed simultaneously at successive said sensing locations when the units are in registry, establishing a signal in response to each sensing of the register marks of a group, and signaling the registry of the operations and thereby the timing of the units relative to each other in dependence on the relationship to each other of the marks of a group. I

15. A method as defined in claim 14 wherein the marks cause a pulse signal at each location and in which the pulse signals are combined to provide output pulses which indicate the registry and thereby the timing of the units, 

1. A method of checking the register of images applied to sheet material passing through a plurality of N units of a multi-unit printing apparatus with the images printed by each unit to be in precise registry with the images printed by the other units, applying a register marking to the material at each of said units with the register marking having a predetermined fixed position relative to the image applied by the unit to the material with the markings applied by the units when the units are in precise registry with each other constituting a group of markings having a predetermined spacing relative to each other, subsequently sensing different numbers of register markings of a said group at each of a plurality of sensing locations along the path of movement of the material as each of the markings move in sequence past each of the sensing locations with the sensing locations being spaced from each other in such a manner that different numbers of said markings of a group arrive at said sensing locations in sequence and each marking of a group is sensed a plurality of different times with successive markings being sensed simultaneously at said plurality of sensing locations when the units are in registry to provide an output signal each time one or more register markings is sensed, using the signals derived from a sequential sensing of different numbers of markings of a group passing said sensing locations to signal the registry of the images and thereby the timing of the printing units relative to each other.
 2. A method as defined in claim 1 wherein said signals are pulse signals, and wherein signals derived from a simultaneous sensing of said markings are combined to provide a combined pulse output for indicating registry.
 3. A method as defined in claim 2 wherein the sensing of the first one of a group of register markings arriving at said sensing locations is used to initiate a display apparatus for displaying the combined pulses and their timed relationship with respect to each other with the number of pulses which are displayed each time a group passes said sensing locations being one less than twice the number of markings in a group.
 4. A method as defined in claim 3 wherein there are N units and the marking of each unit is sensed N times.
 5. A method as defined in claim 1 wherein the images of each printing unit are printed from printing plates and the register markings are on the printing plates of each unit.
 6. A method as defined in claim 1 wherein the register markings are printed with equal spacing between the adjacent markings of a group when the units are in registry.
 7. In a printing apparatus having a plurality of printing units through which sheet material to be printed passes, each of said units having an image carrying member which carries the image to be printed by the unit and each of said image carrying members having as part of the image carried thereby a register mark which is located in a predetermined position with respect to the image, the images printed by the individual units being superimposed on each other and the register marks on the image carrying members of the units being located on the image carrying member so that the register marks are printed adjacent the superimposed image along an imaginary line which extends lengthwise of the sheet material with the register marks having a predetermined spacing relative to each other when the units are printing in precise registry with each other, the register marks consisting of one mark for each unit as sheet material passes therethrough constituting a group of marks, sensing means comprising a plurality of sensing devices, one for each unit, located at respective locations along the path of travel of the sheet material with the sensing devices being spaced from each other by said predetermined spacing wherebY each of said marks pass each of said devices in sequence and are sensed by each said device to provide an output signal in response to each mark with successive marks being sensed simultaneously by successive sensing devices when said units are printing in precise registry with each other, and electrical means responsive to said output signals generated by one group of marks passing all of said devices for signaling the register condition and thereby the timing of said units.
 8. A printing apparatus as defined in claim 7 wherein said signals are pulses and said electrical means comprises circuit means for summing the pulse outputs from said devices.
 9. An apparatus as defined in claim 8 wherein said electrical circuit means comprises a cathode ray tube for displaying said summed output and a sweep circuit activated in response to a pulse output signal from the sensing device first responsive to a register mark of a group of register marks.
 10. An apparatus as defined in claim 8 wherein said electrical means comprises a cathode ray tube for displaying said summed pulses.
 11. An apparatus as defined in claim 10 wherein said electrical means includes means responsive to the speed of the apparatus for maintaining the summed pulses in positions on the tube which are independent of the speed of the material moving through the apparatus.
 12. A method of checking the registry of a plurality of N units operating for performing operations in sequence on material passing through the units, applying a respective register marking to the material with each of said units to thereby provide a group of markings for indicating the registry of the units, sensing the time of arrival of the markings as the markings arrive at a plurality of sensing locations corresponding in a number to the number of units with the marking applied by each unit being sensed a plurality of times in combination with different numbers of markings of said group of markings to provide a group of electrical signals which are analyzable to determine registry.
 13. A method of checking the register of operations performed in sequence on material passing through a plurality of units of a multi-unit apparatus with the operations performed by each unit to be in precise registry with the operations performed by the other units, said method including the steps of applying a plurality of spaced apart register marks to the material as the material passes through the plurality of units of the multi-unit apparatus with the spacing between the marks varying as a function of variations in the registry operations performed by the units, generating a plurality of pulses having a time relationship which is a function of the spatial relationship between the register marks and the registry of the operations performed by the units, combining at least some of said pulses to form a combined pulse having a characteristic which varies as a function of variations in the time relationship between the combined pulses and which is indicative of the registry between the units, said step of combining at least some of said pulses includes the steps of combining a plurality of pulses to form a plurality of combined pulses each of which has a characteristic which varies as a function of the time relationship between the pulses which were combined to form it, forming a series of pulses which includes a plurality of said combined pulses and which has predetermined characteristics which vary with variations in registry between the units in a manner which is indicative of which unit of the plurality of units is out of registry upon a variation in registry, and sensing the predetermined characteristics of the series of pulses to determine which unit of the plurality of units is out of registry upon a variation in registry.
 14. A method of checking the register of operations performed in sequence on material passing through a plurality of units of a multi-unit apparatus with the operations performed by each unit to be in precise regiStry with the operations performed by the other units, applying a register mark to the material at each of said units with the marks applied by the units when the units are in precise registry with each other constituting a group of marks having a predetermined spacing relative to each other, sensing each of the register marks of a group at each of a plurality of sensing locations along the path of movement of the material after said operations have been performed and as the marks move in sequence past each of the sensing locations with the sensing locations being spaced by said predetermined spacing with successive marks being sensed simultaneously at successive said sensing locations when the units are in registry, establishing a signal in response to each sensing of the register marks of a group, and signaling the registry of the operations and thereby the timing of the units relative to each other in dependence on the relationship to each other of the marks of a group.
 15. A method as defined in claim 14 wherein the marks cause a pulse signal at each location and in which the pulse signals are combined to provide output pulses which indicate the registry and thereby the timing of the units. 